Rotary drying drum

ABSTRACT

A rotatably mounted cylindrical drier drum having a steam supply connection for directing steam into the drum and a condensate removal connection for removing condensate out of the drum, the drum being provided with a plurality of bars extending lengthwise of the drum and disposed on the internal surface of the drum for giving turbulence to the condensate in the drum, with the bars being spaced from each other from a spacing of 2.5 inches to a spacing of 7.4 inches with each of said spacings being multiplied by square root d/2.2, where d is the internal diameter of the drum in feet.

Unite States Pa Appel et al. 1 Apr. 3, 1973 54] ROTARY DRYING DRUM 3,217,426 11/1965 Barnscheidt et al ..34 124 x [75] Inventors: David w. Awe; sung Ho Hung, 3,223,133; 12 1967 Webb ..34 124 both of Neenah, Wis.

1/1968 Dickens et al ..34/l24 [7 3] Assignee: Kimberly-Clark Corporation, Nee- Primary ExaminerWilliam E. Wayner nah,Wis. Attorney-Daniel J. H'anlon, Jr. and Raymond J.

Mill 1' 22 Filed: Feb. 16, 1971 e [21] Appl. No.: 115,815 [57] ABSTRACT Related s Application Data A rotatably mounted cylindrical drier drum having a 1 steam supply connectlon for directing steam mto the [63] Continuation of Ser. No. 720,055, April 10, 1968, drum and a condensate removal connection for abandoned' removing condensate out of the drum, the drum being provided with a plurality of bars extending lengthwise [52] U.S.Cl ..34/124, 165/89 of the drum and disposed on the internal Surface of [51] Int. Cl ..F25d 11/02 the drum for giving turbulence to the condensate in [58] F'eld Search 90; 34/119 the drum, with the bars being spaced from each other 34/125 from a spacing of 2.5 inches to 'a spacing of 7.4 inches Ci d with each of said spacings being multiplied by [56] References te \/dl2.2, where d is the internal diameter of the drum UNITED STATES PATENTS feet- I 1,311,431 7/1919 Adt ..165/91 12 Claims, 12 Drawing gu es 2,259,024 10/1941 Cleveland ..l65/91 X 10 48 r? ea 5Q 51 5 r F 7 1 I i 52 x 5 A 46 y B Gg) 47 C E D L 9 F K J I H 3 P'ATENTEDAPR3 ma SHEET 1 BF 6 omh Cir- 'PATENTEBAPR 3 I975 SHEET 2 BF 6 PATENTEDAPR 3 I975 SHEET 3 BF 6 ROTARY DRYING DRUM This application is a continuation of co pending US. application Ser. No. 720,055, filed Apr. 10, 1968, now abandoned.

The invention relates to drier drums for papermaking machines.

The drying section of a papermaking machine generally includes a series of drier drums, each of which has a cylindrical shell, spaced heads extending across the shell to close the open ends thereof, journals for rotatively mounting the shell, conduits for introducing steam into the shell and conduits for withdrawing steam condensate from the shell. The paper web travels from one of these drier drums to the others in such a drying section. Particularly for lightweight paper webs, a so-called Yankee drier drum is utilized. A Yankee drier drum also comprises a cylindrical shell and spaced heads and is generally of the same construction as the drier drums previously mentioned; however, a Yankee drier drum is ordinarily of substantially greater diameter, and only one of these drums is generally used in a papermaking machine. However, with either type of drum, either the smaller type or the large Yankee type, there are certain operating limitations due to the collection of steam condensate in the drum.

The interior of such a drier drum has steam admitted to it so that the drier shell is heated for drying the paper web traveling over the shell. Water condensate forms within the shell as the steam gives off its heat to the shell; and, at low speeds, the condensate pools within the bottom part of the drum. At higher speeds, such as above 1,000 feet per minute peripheral speed of the drums at which most of the drums nowadays are run, the condensate rims within the drier shell, tending to collect in a cylindrical layer about the complete internal periphery of the shell. Although the condensate layer is at steam temperature, heat transfer through the condensate layer is relatively slow, since the body of steam condensate within the drum keeps the steam away from direct action on the drier shell. Thus, as these drier drums are ordinarily operated, the layer of condensate within the drier shell is kept at a minimum thickness for maximum heat transfer.

' It has also been found that, in addition to the rimming effect of the condensate at higher drier speeds, the condensate also oscillates circularly about the internal surface of the drum. The cause of the oscillation is the force of gravity which alternately retards and accelerates the water ring within the drum. The downward movement or collapse of the condensate ring as one part of the oscillation of the ring occurs when the centrifugal force due to rotation of the drum becomes smaller than the terrestrial acceleration or that due to gravity.

The periodical Das Papier," Volume 14, No. 10a, of October, 1960 (pages 600-609), in an article written by Barnscheidt and Schadler, gives a description of this oscillating movement of condensate in a steam heated cylinder or drier drum, and the authors of this article describe therein the use of rails or bars within the drum for increasing condensate turbulence to increase heat flow through the condensate. These bars extended longitudinally for the complete length of the drum and were fixed in place by means of circular rings provided with turnbuckles for expanding the rings to thereby hold the bars tightly in contact with the interior surface of the drum. According to the authors, these bars were slotted on their outer surfaces in contact with the internal surface of the drum; and, for a drum of 1.5 meters or about 5 feet in diameter, 18 rails was an optimum so that these rails were spaced on approximately 10-inch centers. According to the article, the rails cause a surface wave associated with oscillation of the condensate within the drier shell, but apparently the spacing of the bars had no relation to the resonance of sloshing in the spaces between the bars; and, indeed, Barnscheidt and Schadler apparently did not realize that under certain conditions a resonance effect might exist. The authors concluded that bars 1 centimeter or 0.393 inch high were best in their drier.

It is an object of the invention to so arrange bars within a drier drum to maximize the turbulence due to the oscillations of the rim of condensate within the drier shell to thereby minimize the retardation of heat flow by the condensate, and preferably this is accomplished by utilizing bars extending longitudinally within the drier shell which are unslotted and are spaced peripherally of the internal shell surface at the particular distances, or substantially at these distances, at which resonant sloshing of the condensate takes place between the bars.

The invention consists of the novel methods, arrangements and devices to be hereinafter described and claimed for carrying out the above stated objects, and such other objects, as will be apparent from the following description of a preferred form of the invention, illustrated with reference to the accompanying drawings, wherein:

FIG. 1 is a longitudinal sectional view of a Yankee drier drum having a series of condensate impeding bars fixed on the inner surface;

FIG. 2 is a sectional view taken on line 22 of FIG.

FIG. 3 is a sectional view on an enlarged scale taken on line 33 of FIG. 2;

FIG. 4 is a partial longitudinal sectional view of a portion of the shell of the drier drum and taken on an enlarged scale;

FIG. 5 is a fragmentary side elevational view of a papermaking machine incorporating the drier drum illustrated in the preceding figures;

FIG. 6 is a sectional view similar to FIG. 2 but schematic in nature and showing the manner in which the water condensate sloshes over the bars inside the drum;

FIGS. 7, 8, 9, and 10 are perspective veiws of the internal surface of the drier drum taken respectively at the 12 o clock, 3 oclock, 6 oclock and 9 oclock positions and also showing the manner in which the water condensate sloshes over the bars;

FIG. 11 is a perspective view of the internal surface of the drier drum showing the manner in which the I water condensate sloshes over the bars inside the drum; and

FIG. 12 is a graph showing the relationship between the heat transfer coefficient and condensate depth for a certain 5-foot diameter drier.

Like characters of reference designate like parts in the several views.

The illustrated drier drum, as may be seen by referring to FIG. 1, comprises a thin cylindrical outer shell 10 and a pair of relatively flat ring-shaped heads 1 1 and 12. The heads 11 and 12 are rigidly secured to the ends of the shell and are supported by a hollow central axle or shaft 13. An integral bolting flange 14 is provided at each end of the shell 10, and each flange mates with a similar peripheral flange 15 on the adjacent head. The rigid attachment of the shell to each head may be made by a plurality of bolts 16 inserted from the inside of the shell and drawn up by nuts on the outside of the head.

A short cylindrical section 17 has a machined bolting flange 18 provided at its inner end and is formed integrally with each of the heads 11 and 12, each section extending longitudinally of the shell 10 and at a radial location which is intermediate the inner and outer edges of the head. A plurality of heavy staying members 19 extend between the heads 11 and 12 longitudinally of the drier, being fixed with respect to the flanges 18 by means of flanges 20 formed on the staying members 19 and bolts 21 extending through the flanges 18 and 20. The staying members 19 control the bowing of the heads 11 and 12 to eliminate stress occurring in the shell 10 at or near its connections to the heads 11 and 12.

The heads 11 and 12 and shell 10 and the central shaft 13 are of cast construction. The shaft 13 is formed in two halves 22 and 23, and the halves are provided with flanges 24 and 25, with bolts 26 extending through the flanges to fix the halves 22 and 23 together. Two separate compartments 27 and 28 are provided within the shaft 13 by means of a separator 29 within the half 22. An enlarged bolting flange 30 is provided near each end of the shaft 13, and each head 11 and 12 is provided with a flange 31 that mates with a flange 30, the flanges 30 and 31 being fixed together by means of bolts 32. Journals 33 are provided on the ends of the shaft 13 for rotatably supporting the drier in suitable bearings, and a shaft extension 34 is provided at one end of the shaft 13 for mounting a driving gear or sprocket or the like. Bores 35 and 36, respectively in with the'compartments 27 and 28, are provided in the shaft 13 at its ends. Bores 35 and 36 may respectively be utilized to provide steam under pressure into the compartment 27 and for withdrawing the steam condensate from the compartment 28.

A plurality of steam supply pipes 37 having rows of steam discharge openings 38 in them may be used for supplying steam under pressure to the interior of the drier drum. The pipes 37 are connected to the compartments 27, and the pipes 37 extend axially with respect to the shaft 13 and may be appropriately fixed adjacent their ends to the shaft 13.

The drier is provided with a condensate withdrawal system which comprises a pair of manifolds 39 and 40 positioned oppositely from each other with respect to the shaft 13 and located adjacent the inner surface of the shell 10. The manifolds 39 and 40 are supported at their ends from the bolting flanges 18 by means of supports 41 and are supported intermediate their ends from the staying members 19 by means of ties 42.

A plurality of equal length small diameter tubes 43 extend radially through each of the manifolds 39 and 40. The tubes 43 have their outer ends 44 terminating closely adjacent the inner surface of the shell 10 and have their inner ends 45 terminating well within the associated manifold close to the longitudinal center of the manifold.

The manifold 40 has a pair of arcuately shaped branch pipes 46 and 47 connected with it, and the manifold 39 has a pair of similar pipes 48 and 49 connected with it. The pipes 46 and 48 are connected together by means of a Y-shaped .fitting 50, and the central leg of the fitting 50 is connected by means of a radially extending pipe 51 with the shaft 13 and particularly with the compartment 28 in the shaft. The pipes 47 and 49 are connected similarly with the compartment 28 utilizing a Y-shaped fitting 52 connected to a radially extending pipe 53. The branch pipes 46, 47, 48, and 49 are supported intermediate their ends by means of support brackets 54 extending between adjacent staying members 19 and tie rods 55 extending between the brackets 54 and the pipes 46, 47, 48, and 49.

A plurality of bars A, B, C, D, E, F, G, H, l, J, K, L, etc., are longitudinally disposed within the shell 10 and are fixed to the internal shell surface. Each of the bars, A, B, C, etc., may be so fixed by means of screws 56 extending through the bar and into the shell 10. A manhole 57 closed by a removable cover 58 is provided in each of the heads 11 and 12 so that work-men may enter the drier drum when stationary and unheated for the purpose of fixing the bars A, B, C, etc., within the shell 10.

The drier drum may be mounted in a papermaking machine as illustrated diagrammatically in FIG. 5. The journals 33 of the shaft 13 may be mounted in bearings 59 which are secured to a supporting frame 60. The wet paper web to be dried is carried by a felt web 61 which travels around felt rolls 62. The paper web is forced against the surface of the drier shell 20 by a pressure roll 63 which is rotatably mounted in brackets 64 attached to arms 65. The arms 65 are each pivoted at 66 to the frame 60, and the pressure roll 63 is forced against the surface of the drier shell 10 by a hydraulic motor 67 which bears against each arm 65.

The dried paper web may be removed from the surface of the drier shell by a creping doctor which includes a doctor blade 68 secured within a doctor blade holder 69. The blade 68 and holder 69may be supported by conventional mechanism including shafts 70 carried by the holder 69 and rotatably mounted within guide blocks 71. The blocks 71 in turn are slidably mounted within a slide assembly 72 attached to a pivot frame 73 carried by the frame 60. Through the slide arrangement provided by the guide blocks 71 and slide assembly 72, the vertical position of the doctor blade 68 can be varied as desired to obtain the best creping angle. The doctor blade holder 69 and the blade 68 are pivoted from a toggle mechanism 74 which is attached through a lever arm 75 to one of the shafts 70. A spring loading mechanism 76 is connected through the toggle mechanism 74 to provide a resilient contact for the doctor blade against the surface of the drier shell 10.

In operation, a moist paper web is directed onto the outer surface of the shell 10, being carried by the felt web 61; and the pressure roll 63, which exerts a substantial pressure on and has a pressure nip with the drier drum, forces the paper web against the outer surface of the shell 10 and causes the paper web to adhere onto the shell 10. A sprocket or other driving mechanism (not shown) on the extension 34 may be utilized for drivingly rotating the drier drum. The web is dried as the drum rotates, and the web is creped off the outer surface of the drum by means of the creping blade 68. Alternately, the paper web may be simply pulled off the surface of the drier drum without the use of such a blade.

Steam under pressure is supplied to the compartment 27 through the bore 35, and the steam enters the internal compartment of the drum through the supply pipes 37 and the openings 38 in the pipes 37. The steam heats the drier drum for drying the paper web; and, as the steam loses heat, it condenses into water. The water condensate remains on the internal surface of the shell and rims or lies completely around the shell due to the action of centrifugal force. The condensate removal system including the manifolds 39 and 40, the small diameter tubes 43 and the condensate withdrawal pipes 46, 47, 48, 49, 51, and 53 remove this condensate.

The tube ends 44 are located very close to the internal surface of the shell 10, and steam within the drier drum rushes to these ends of the tubes, since the pressure within the tubes and in the connected manifolds 39 and 40 is lower than the pressure of the steam within the drum. The steam, in entering the ends 44 of the tubes 43, sweeps across the inner surface of the drier drum and atomizes the condensate existing on the inner drum surface. Thus, a steam-water mixture passes radially inwardly through the bores of the tubes 43 into the manifolds 39 and 40.

Some of the steam condenses as it passes through the tubes 43, but the pressure of the steam within the drier drum is sufficient to move the water-steam mixture inwardly; and some condensation takes place also within the manifolds 39 and 40. The water condensate tends to collect on the outer walls of the manifolds 39 and 40 and moves from these outer walls into the pipes 46, 47, 48, and 49 and moves from these last mentioned pipes into the compartment 28 through the fittings 50 and 52 and the radially extending pipes 51 and 53.

The steam condensate withdrawal system is substantially that disclosed in Joseph B. Webb US. Pat. No. 3,359,647; and this patent may be referred to for more details of the withdrawal system.

Assuming that the drier drum is rotating at relatively high speeds, such as 1,000 feet per minute peripheral speed or greater, the drier condensate tends to rim the drum completely around the drum; and this rimming is accompanied by oscillation of the condensate circularly about the internal surface of the drum. This oscillation is apparently caused by the force of gravity, alternately retarding and accelerating the water ring within the drum. As the water ring oscillates in the drum, it flows over the bars A, B, C, D, etc.; and these bars give turbulence to the condensate and thereby increase the heat flow and the condensate heat transfer coefficient (BTUs per hour per square foot per degree Fahrenheit) from the steam through the drier shell 10.

The condensate layer thus rendered turbulent is reduced from a uniform thickness layer to one that is of very non-uniform thickness, allowing greater heat transfer; and, in addition, the turbulent flow of the condensate apparently scrubs off a water film from the interior surface of the drier increasing heat transfer. The height of the various bars A, B, etc., is preferably maintained sufficiently small so that the condensate sloshes over the bars not only for increasing the turbulence but also for allowing the condensate to flow to the tubes 43 which are disposed in two opposite longitudinal rows on the internal surface of the drum.

According to the invention, the bars A, B, etc., are separated peripherally within the shell 10 by such a particular distance that causes a resonance of sloshing in the spaces between the bars A, B, etc., so that the condensate in its oscillations rises to maximum height at the bars A, B, C, etc. As will be hereinafter pointed out, substantially smaller or larger spacings between the bars, although giving some improved heat transfer over the condition in which no bars are used, nevertheless result in reduced turbulence in the condensate and reduced heat transfer. In this connection, it may be mentioned that preferably a minimum average thickness of condensate is usedin the drum, inasmuch as the condensate is a poor conductor of heat; and we contemplate that the average condensate thickness shall preferably be about 1 millimeter or 0.040 inch.

Our theoretical studies of condensate behavior in cylindrical drier shells indicate that the optimum spaction:

f,,= 1/211 w/g' 1r/a tanh (1r h)/a Eq.l in which g is the radial acceleration, a is the length of the space or spacing between adjacent bars A, B, C, etc. measured peripherally within the shell, and h is the average depth of the condensate.

If h/a is small, as is the case, then:

tanh 1r hla= 11 Ma Eq. 2 Therefore, substituting the value of tanh 'rr h/a from Equation 2 into Equation 1:

f 1/ h/ Eq. 3 The acceleration (g') due to rotation is:

g' S IR Eq. 4

in which S is the peripheral velocity of the inside surface of the shell 10 and R is the inside radius of the shell 10.

Substituting the g from Equation 4 into Equation 3 gives the natural frequency of sloshing in one compartment between adjacent bars A, B, etc.,- which is:

fl V s Eq. 5 The frequency of rotation of the drier shell 10 isi fa sI Eq. 6

will slosh over and reach maximum depth on one side of each bar, will reverse direction and will slosh over and reach maximum depth on the other side of the bar and will again reverse direction and will reach maximum depth and slosh over the first mentioned side of the bar. lff, equals f this time period equals the time required for each revolution of the drum, and this sequence for each bar occurs once for each revolution of the drum.

Assuming f, =f the righthand portions of Equations 5 and 6 may be equated so as to produce the following equation:

Equation 7 TABLE 1 External Drier lnternal Drier Condensate Bar Diameter Diameter Depth Spacing (Millimeters) (lnches) 3 ft. 2 ft., 10 in. 1.0 (0.040 in.) 2.6 1.5 (0.060 in.) 3.2 2.5 (0.100 in.) 4.1 3.0 (0.120 in.) 4.5 4 ft. 3 ft., 10 in. 1.0 3.0

1.5 3.7 2.5 4.8 3.0 5.2 5 ft. 4 ft., 10 in. 1.0 3.4 1.5 4.2 2.5 5.4 3.0 5.9 12 ft. 11 ft., 8 in. 1.0 5.2 1.5 6.4 2.5 8.3 3.0 9.1 16 ft., 6 in. 16 ft., 2 in. 1.0 6.2

1.5 7.6 2.5 9.8 3.0 10.7 18 ft. 17 ft., 8 in. 1.0 6.4 1.5 7.9 2.5 10.2 3.0 11.1

Actual experimental operating results verify some of the values given in the above table. Drier condensate heat transfer coefficients were determined experimentally using a 5-foot drier (inside drier diameter of 4 feet, 10 inches) with an average condensate thickness of 0.1 inch (2.5 mm.) and some data from this experiment are tabulated below.

TABLE 2 Condensate Heat Transfer Coefficient (BTU/hr. ft. F.)

2.75-Inch 5.75-Inch l 1.75-lnch Drier Bar Spacing Bar Spacing Bar Spacing (No Speed Solid Slotted Solid Slotted Solid Slotted Bars) 1,300 fpm 830 1,450 1,000 950 700 450 1,800 fpm 860 680 700 420 270 2,600 fpm 740 380 490 280 110 The drier used in the experiment had an external diameter of 5 feet and an internal diameter of4 feet, 10 inches. The figures under the headings Slotted give the heat transfer coefficients for conditions in which the bars, in lieu of being continuous along their edges in contact with the inner drum surface, were instead slotted, as suggested in the Das Papier" article; and the slots used were 1.5 inches long, with 0.5 inch lands in actual contact with the internal drum surface. The condensate heat transfer coefficients are given in BTUs per hour per square foot per degree Fahrenheit; and the higher the coefficient is, the greater is the heat transfer through the drier. Table 2 shows that, at 1,300 feet per minute internal peripheral drier speed, the maximum heat transfer coefficient of 1,450 was obtained with a spacing between solid bars of 5.75 inches which is very close to the theoretical bar spacing of 5.4 inches indicated in Table 1, for 0.1 inch or 2.5 millimeters of condensate depth for a drier drum of this size. Table 2 also shows that, at this drier speed, the coefficient decreased to 950 using solid bars spaced 11.75 inches apart, so that the coefficient was only about percent of that obtainable at the 5.75 inch spacing. The coefficient was still less when the spacing between bars was substantially halved to 2.75 inches, being only 830 or about 57 percent as at the 5.75 inch spacing. With no bars being used at this speed, the coefficient decreased to 450. Similarly, the slotted bars gave only 69 and 48 percent (coefficients of 1,000 and 700) of the heat transfer coefficient using solid bars at 5.75 inch spacing. Table 2, as will be noted, also indicates substantial reductions in coefficient at higher speeds of the drier in cases in which the bars were slotted or were increased in number, or in cases in which no bars were used; and in fact, the table shows that the use of solid bars at 5.75 inch spacing (approximating the 5.4 inch spacing shown in Table 1 for the same conditions)for the higher speed of 2,600 fpm, causes the coefficient to increase nearly to 7 times that for the condition in which no bars are used (a change in coefficient from 1 10 to 740).

FIG. 12 shows graphically some of the experimental results set forth in tabular form in Table 2. It will be observed that with the bars at 5 34 inches spacing, the heat transfer coefficient for 1,300 feet per minute drier speed rises, as the condensate depth is increased, to a maximum at about 2.5 millimeters condensate depth; and, as the condensate depth is increased beyond 2.5 millimeters, the heat transfer coefficient falls. The curve of heat transfer coefficient for a drier speed of 1,800 feet per minute is similar to that for 1,300 feet per minute drier speed but is lower, corresponding to lower heat transfer coefficients; and the curve for a drier speed of 2,600 feet per minute is quite similar to those for the lower drier speeds but indicates still lower heat transfer coefficients. All of these three curves peak at about 2.5 millimeters at which the condition of resonant condensate reciprocation between the bars occurs (it may be noted from Equation 7 that the spacing between bars at which this condition occurs is independent of drier speed and varies only with the inside radius of the drier and the average depth of the condensate). The condensate tends to become more quiescent as the drier speed is increased, and this is the principal reason why the curves for the higher drier speeds are lower on the graph than those for the lower drier speeds.

Curves showing the heat transfer coefficient for a plain shell drier are also shown in the FIG. 12 graph. Condensate oscillation occurs in a plain shell drier as well as in the drier'of the invention having the bars A, B, C, etc. fixed on its internal surface, but since in a plain shell drier there is nothing to give substantial turbulence to the condensate as it oscillates, the heat transfer coefficients for a plain shell drier are substantially lower than for the driers of the invention provided with the internal bars A, B, C, etc. It will be observed that, for a plain shell drier, the heat transfer coefficients for 1,300 feet per minute drier speed are substantially less than the heat transfer coefficients for the drier provided with the internal bars at this same speed;

1 and the curve for the plain shell drier at 1,300 feet per minute does not peak at any particular condensate depth. The curves for 1,800 feet per minute and 2,600

feet per minute for a plain s'hell drier are even lower than that for the plain shell drier shell drier at 1,300 feet per minute, and the latter two curves also do not peak at any particular condensate depth.

The curve titled Theoretical LaminarFilm is calculated for the condition'in which no oscillation occurs in a plain shell drier, such as, for example, at very high peripheral speeds; and it will be observed that the other curves of heat transfer coefficient, particularly for the condition in which bars are provided, are very much higher on the graph corresponding to very substantially greater heat transfer coefficients.

With respect to the heights of the bars A, B, C, etc., our analysis does not indicate any particular optimum height but an approximate desirable range can be identified. When the bars are spaced as preferred and as above described, such that sloshing occurs at or near resonant frequency for the waves in the compartments between the bars A, B, etc., then the fluid piles up first at one end of each compartment and then at the other end. The height of the mass of condensate when it sloshes against either side of each bar should be greater than the height of the bar so that some of the condensate spills over the bar into the next compartment, and this spillage causes the'condensate to migrate around the internal surface of the shell toward the condensate withdrawal tubes 43, assuming that between 25 to 50 percent of the condensate originally in a compartment between adjacent bars A, B, etc., spills over a bar into the next compartment. For these purposes, we have found that the height should be between 1.5 and 7.5 times the average condensate depth in the drier; and we prefer that the bar height should be between two and three times the average condensate depth for rapid migration of condensate in the drier, although substantial improvement in heat transfer can be expected for bar heights between 1.5 and 4 times the average condensate depth.

It will be understood that the average condensate depth can be regulated by moving the outer ends 44 of the tubes 43 toward and way from the internal surface of the shell 10; and preferably the tube ends 44 shall be located so close to the internal surface of the shell 10 that the average condensate depth is no greater than 3 millimeters, inasmuch as thicker condensate layers would cause an unduly great retardation of heat flow. Due to the possibility of hot spots near the ends 44 of the individual siphon tubes 43, it is preferred that the condensate depths used shall not be less than 1 millimeter or 0.040 inch.

since the average condensate depth is preferably between I millimeter and 3 millimeters, the permissible bar heights mentioned above are between 1.5 millimeters and 22.5 millimeters, more preferably between 1.5 millimeters and 12 millimeters, and still more preferably between 2 millimeters and 9 millimeters. These heights correspond, respectively, to the range of 1.5 to 7.5, the range of 1.5 to 4 and the range of two to three times the average condensate depth mentioned above.

FIGS. 6 to 11 are provided for the purpose of illustrating the manner in which the condensate travels within the various compartments defined by the bars A, B, C, etc., as the drier drum rotates, with the bars being spaced at or approximately at the spacings providing of bars indicated in FIGS. 6 to '11 has been reduced to 16 to better illustrate diagrammatically the flow of condensate with the drier drum.

At the 12 oclock position of the drum, that is, at the position .at the uppermost portion of the periphery of the shell 10, the water condensate in the compartment between adjacent bars AA, BB, etc., is piled up against the trailing bar defining this compartment. The shell 10 is shown as rotating in the clockwise direction, and the leading bar of any particular compartment defined by adjacent bars AA, BB, etc., is that bar arriving first at the 12 oclock position while the trailing bar of the compartment is that bar arriving subsequently at the 12 oclock position. Some slight sloshing or spilling over the trailing bar at this position takes place, but most of this sloshing over the trailing bar has taken place previously in the quadrant between the 9 oclock and 12 oclock positions as will be hereinafter described in greater detail. At the 6 oclock position, water condensate is piled up against the leading bar AA, BB, etc., of the compartment defined by adjacent bars, and sloshing over the leading bar occurs to a slight extent, but most of the sloshing over this bar has taken place previously in the 3 to 6 oclock quadrant as will be hereinafter described in greater detail.

More particularly, as a compartment defined by adjacent bars AA, BB, etc., moves from the l2'oclock position to the 6 oclock position through the 3 oclock position, condensate moves from the trailing bar of the compartment toward the leading bar; and, by the time the compartment reaches the 3 oclock position, the condensate has adtually reached the leading bar and starts to spill or slosh over the leading bar. This spilling over the leading bar continues until the 6 oclock position is reached; however, this spilling is at a maximum rate between approximately the 3 oclock position and the 4:30 oclock position. From the 4:30 oclock position to the 6 oclock position, the condensate reduces its spilling effect and tends to pond against the leading bar with decreasing spillage over the bar.

This effect is substantially reversed as, a compartment moves from the 6 oclock position to-the 12 oclock position through the 9 oclock position; and, with this rotation, the condensate in each compartment moves from the leading bar toward the trailing bar of each compartment. The principal movement of the condensate across the compartment is between the 6 oclock and the 9 oclock positions, and the condensate reaches the trailing bar approximately at the 9 oclock position and starts spilling over the trailing bar. The greatest quantity and rate of spillage across the trailing bar of a compartment takes place between the 9 oclock and 10:30 oclock positions, and the spillage reduces as the compartment subsequently approaches the 12 oclock position, with the spilling ceasing and with the condensate simply ponding up against the trailing bar as the compartment reaches the 12 oclock position.

As has been hereinbefore explained, the spillage of the condensate from the individual compartments is due to the effect of gravity; and, with resonant conditions existing, the spillage or sloshing over at individual bars takes place constantly at the same positions within the drum; and the other conditions of the condensate within the drum as described above, such as movement of condensate from one side of a compartment to the other side, exist constantly at the same positions in the drum.

As is quite clear from the above description, for example from Equation 7, the spacing between adjacent bars A, B, etc., is determinative of whether or not resonant conditions exist for any particular condensate depth. The width of the bars A, B, etc., is quite immaterial insofaras the condensate motion within the drier shell is concerned; however, if a bar is too wide, it has an undesirable insulating effect with respect to the outer shell surface which would produce a wet streak in the paper being dried. Each of the bars A, B, etc. should, therefore, be considerably narrower than the thickness of the drier shell. The drier shell may have a thickness of from 1 /4 inches to 2 inches, for example, and the width of a bar may thus well be one-half inch or less and should preferably be three-eighths inch to onehalf inch. In this connection, it is apparent that the bars A, B, etc. should have sufficient stock in them so that screws 56 of sufficient strength may pass through the bars.

It will be noted that the FIG. 12 curves of heat transfer coefficient using spaced bars at various drier speeds, do peak; however, the peaks are not sharp. Therefore, even if exact resonant conditions do not occur within a drier using the bars A, B, etc., for the reason that the bar spacing does not exactly correspond with that derived from Equation 7 for the particular condensate depth that is used, nevertheless substantial improvement in heat transfer may be obtained by using the bars A, B, etc. Thus, the bar spacings derived from Equation 7 may be varied by :25 percent, and the maximum and minimum bar spacings set forth in Table l for each diameter of drier may be respectively decreased by 25 percent and increased by 25 percent, while still obtaining substantial advantages from the use of the bars A, B, etc. Thus, the 5-foot drier, for example, which, according'to Table 1 has bar spacings of 3.4 inches to 5.9 inches for resonant conditions, corresponding to the preferred condensate depth of l to 3 millimeters, may utilize bar spacings that vary from 0.75 times 3.4 inches or 2.5 inches to 1.25 times 5.9 inches or 7.4 inches. We do not particularly favor, how ever, reductions in bar spacings from the minimum values indicated for each of the various drier sizes, since this expedient increases the cost of the bars and their installation.

Although we have illustrated the bars A, B, C, etc., which are separate parts and are fastened by means of the screws 56 within the shell 10, it is within the contemplation of the invention that the bars A, B, etc., may be formed integrally with the shell 10, if desired. Also, the bars A, B, etc., need not extend absolutely parallel with the axis of the shell 10 butmay be made to extend in a shallow spiral within the shell 10 while still obtaining the advantages of the invention.

It is apparent from Equation 7 that the bar spacing according to the invention varies as the square root of the inside radius of the shell 10 and, therefore, as the square root of the inside diameter of the shell 10. Therefore, if it is desired to convert any of the bar spacings for one size of drum to corresponding spacings for another size, this may be done by means of proportions. For example, as above mentioned, the bar spacings according to the invention for a 5.-foot drier vary from 3.4 inches to 5.9 inches 1- 25 percent or from 2.5 inches to 7.4 inches. In order to convert these barspacings for the 5-foot drum (having an internal diameter of 4 feet, 10 inches or 4.83 feet) to the values for obtaining the same resonance conditions and condensate turbulence for a l6 k-foot drier (with an internal diameter of 16 feet, 2 inches or 16.16 feet), calculations may be made as follows:

Bar spacing range (2.5 to 7.4) V d/2'.2 inches.

Carrying out the indicated division gives:

Bar spacing range 1.1 {Ito 3.4 w/F where d is expressed in feet.

The bar spacing according to the invention includin the i 25 percent tolerance and based on thepreferred condensate depths thus are:

External Drier Internal Drier Bar Spacing Diameter Diameter (Inches) 3 ft. 2 ft., 10 in. 1.9 to 5.6 4 ft. 3 ft., I0 in. 2.2 to 6.5

5 ft. 4 ft., in. 2.5 to 7.4 1211. 11 ft., 8 in. 3.9 to 11.4 16 ft., 6 in. 16. ft., 2 in. 4.6 to 13.5 18 a. 11m, 8 in. 4.3 to 13.9

The spacing of the bars "A, B, etc., according to Equation 7 or with the spacings set forth in Table 3, assures substantial increases in heat transfer through a drier drum as contrasted to the condition in which no .bars are utilized, and the results are particularly satisfactory if solid bars are used as contrasted to bars which have slots in their faces adjacent to the inner surface of the drier shell. The bars A, B, etc., are preferably, as illustrated, of rectangular cross section for this purpose and are easily and firmly attached onto the inner surface of the shell 10 by means of the screws 56.

Although we have described our improved drier drum in connection with a source of steam for heating the drum, our drum may also be used with other condensible heating fluids;for example, with Dowtherm and Dowtherm A which are particularly described in US. Pat. No. 3,363,328 for Rotary Drying Drum, issued Jan. 16, 1968', to one of the present joint inventors, Sung Ho Hong, and to another joint inventor, William A. Dickens. As is mentioned insaid prior U.S. Pat. No. 3,363,328, particularly in column 2, lines 27 to 59 of the patent, these fluids termed Dowtherm E and Dowtherm A have higher condensing temperatures than water and may thus supply more heat to a drier drum.

We wish it to be understood that the invention is not to be limited to the specific constructions and arrangements shown and described, except only insofar as the claims may be so limited, as it will be understood to those skilled in the art that changes may be made without departing from the principles of the invention.

We claim:

1. A hollow cylindrical drier drum for operation at peripheral speeds of 1,300 feet per minute or more having journals for rotatably mounting the drum, a steam supply connection for directing steam into the drum, a condensate removal connection for removing condensate out of the drum, and a plurality of bars extending lengthwise of the drum and disposed on the inside surface of the drum for giving turbulence to the condensate in the drum, said bars being spaced from each other byaperipher al distance in the rangeof 1.1

VJ inches to 3.4 /d inches where d is the Tat 5115? diameter of the drum in feet, the spacing of said bars being such that condensate sloshing between bars in therotation of the drum resonates.

2. A hollow cylindrical drier drum as set forth in claim 1, the height of said bars being between 1.5 millimeters and 22.5 millimeters.

3. A hollow cylindrical drier drum as set forth in claim 1,the height of said bars being between 2 millimeters and 9 millimeters.

4. A hollow cylindrical drier drum as set forth in claim 1, said bars being rectangular in cross section.

5. A hollow cylindrical drier drum as set forth in claim 1, said bars being integrally separate from the drum and being fixed to the inside surface of the drum by means of screws.

6. A hollow cylindrical drier drum as set forth in claim 1, said bars being integrally separate from the drum and fixed on the mner drum surface and each bar having an unbroken surface in contact with the inner drum surface.

7. A hollow cylindrical drier drum having journals for rotatably mounting the drum, a. steam supply connection for directing steam into the drum, a condensate removal connection for removing condensate out of the drum, means for maintaining a predetermined average thickness of rimming condensate in the drum, and a plurality of bars extending lengthwise of the drum and disposed on the inside surface of the drum for giving turbulence to the condensate in the drum, said bars being spaced from each other by a distance determined by the following formula: a (l i 0.25 )11' w/ Rh, where a is the spacing between adjacent bars, R is the inside radius of the drum and h is the average depth of the condensate.

8. A hollow cylindrical drier drum as set forth in claim 7, the height of said bars being between 1.5 millimeters and 22.5 millimeters.

9. A hollow cylindrical drier drum as set forth in claim 7, the height of said bars being between 2 millimeters and 9 millimeters.

10. A hollow cylindrical drier drum as set forth in claim 7, said bars being rectangular in cross section.

11. A hollow cylindrical drier drum as set forth in claim 7, said bar s being integrally separate from the drum and being fixed to the inside surface of the drum by means of screws.

12. A hollow cylindrical drum DRUM as set forth in claim 7, said bars being integrally separate from the drum and fixed surface the inner drum surface and each having an unbroken SURFACE'in contact with the inner drum surface. 

1. A hollow cylindrical drier drum for operation at peripheral speeds of 1,300 feet per minute or more having journals for rotatably mounting the drum, a steam supply connection for directing steam into the drum, a condensate removal connection for removing condensate out of the drum, and a plurality of bars extending lengthwise of the drum and disposed on the inside surface of the drum for giving turbulence to the condensate in the drum, said bars being spaced from each other by a peripheral distance in the range of 1.1 square root d inches to 3.4 square root d inches where d is the internal diameter of the drum in feet, the spacing of said bars being such that condensate sloshing between bars in the rotation of the drum resonates.
 2. A hollow cylindrical drier drum as set forth in claim 1, the height of said bars being between 1.5 millimeters and 22.5 millimeters.
 3. A hollow cylindrical drier drum as set forth in claim 1, the height of said bars being between 2 millimeters and 9 millimeters.
 4. A hollow cylindrical drier drum as set forth in claim 1, said bars being rectangular in cross section.
 5. A hollow cylindrical drier drum as set forth in claim 1, said bars being integrally separate from the drum and being fixed to the inside surface of the drum by means of screws.
 6. A hollow cylindrical drier drum as set forth in claim 1, said bars being integrally separate from the drum and fixed on the inner drum surface and each bar having an unbroken surface in contact with the inner drum surface.
 7. A hollow cylindrical drier drum having journals for rotatably mounting the drum, a steam supply connection for directing steam into the drum, a condensate removal connection for removing condensate out of the drum, means for maintaining a predetermined average thickness of rimming condensate in the drum, and a plurality of bars extending lengthwise of the drum and disposed on the inside surface of the drum for giving turbulence to the condensate in the drum, said bars being spaced from each other by a distance determined by the following formula: a (1 + or -0.25) pi Square Root Rh, where a is the spacing between adjacent bars, R is the inside Radius of the drum and h is the average depth of the condensate.
 8. A hollow cylindrical drier drum as set forth in claim 7, the height of said bars being between 1.5 millimeters and 22.5 millimeters.
 9. A hollow cylindrical drier drum as set forth in claim 7, the height of said bars being between 2 millimeters and 9 millimeters.
 10. A hollow cylindrical drier drum as set forth in claim 7, said bars being rectangular in cross section.
 11. A hollow cylindrical drier drum as set forth in claim 7, said bars being integrally separate from the drum and being fixed to the inside surface of the drum by means of screws.
 12. A hollow cylindrical drum DRUM as set forth in claim 7, said bars being integrally separate from the drum and fixed surface the inner drum surface and each having an unbroken SURFACE in contact with the inner drum surface. 